Fatty acid alkyl esters derived from vegetable oils are used as cooking oil and, in addition, used in such fields as cosmetics and pharmaceuticals. In recent years, attention has been paid to uses as additives to fuels such as gas oil. For example, fatty acid alkyl esters are added to gas oil in an amount of several percents as vegetable-derived biodiesel fuel for reducing emission of CO2. Glycerin is mainly used as a raw material for nitroglycerin and is further used as a raw material for alkyd resins, or for pharmaceuticals, foods, printing inks, cosmetics and the like. As a method for producing such fatty acid alkyl esters and/or glycerin, transesterification of alcohols with triglyceride which is a main component of fats and oils is known.
In carrying out such a production method on a commercial scale, a homogenous alkaline catalyst is generally used.
However, the method needs complicated steps in order to separate and remove the catalyst from the reaction system. Also, the alkaline catalyst causes saponification of free fatty acids contained in the fats and oils. Therefore, soaps are produced as a byproduct, which needs a step of washing the produced soaps with large amounts of water. In addition, the yield of fatty acid alkyl esters decreases due to the emulsifying effect of the soaps and, in certain instances, the subsequent glycerin purification process becomes complicated.
Korea Patent No. 415396 discloses, as a prior art of producing glycerin and/or a fatty acid alkyl ester using a natural fat or oil, a method for producing a fatty acid ester, including the steps of: bringing a plant and animal fat or oil into contact with an alcohol equal to 2 to 40 times the fat or oil in molar ratio at 60 to 200° C. for 0.5 to 18 hours in the presence of a metal oxide catalyst that is magnesium oxide (MgO) or manganese oxide (MnO) which accounts for 0.1 to 10% by weight relative to the fat or oil, thereby preparing a mixture of a fatty acid ester with glycerin; and separating the mixture into each component. WO 1998/56747 discloses a method of performing transesterification of triglyceride derived from a plant or an animal with mono- or polyalcohol in the presence of an heterogeneous solid catalyst, wherein aluminum, chromium, magnesium, zinc, calcium, copper, manganese, or a mixed oxide derived from them is used as the heterogeneous solid catalyst.
However, these technologies have still room for contrivance in order to more improve a life of the catalyst, thereby suppressing a reduction in activity of the catalyst or purity of a generated product due to leaching of an active component of the catalyst. Further, according to these technologies, free fatty acid (FFA) and/or water contained in a starting material further reduces the life of the catalyst. Therefore, these technologies also have room for contrivance in order to suppress the reduction in activity in such a case.
WO 2005/35479 discloses the following production method of a fatty acid monoester and a polyalcohol, wherein a polyalcohol is transesterified with a compound selected from the group consisting of an animal fat or oil, a plant fat or oil, and a fatty acid methyl ester, thereby producing a fatty acid monoester and a polyalcohol, wherein a solid base catalyst is used as the catalyst, and the solid base catalyst is selected from the group consisting of a metal oxide of monovalent and trivalent elements, a metal oxide of divalent and trivalent elements, and a mixture thereof. According to this technology, a fatty acid monoester and a polyalcohol are produced using a solid base catalyst including a specific element. However, this technology has a problem in that a catalyst component leaches out during the reaction, which shortens the life of the catalyst. Therefore, there is room for contrivance in order to suppress the reduction in activity, caused by the leaching of the active component.
In a conventional method for solving the above-mentioned problems, in order to suppress a reduction in purity of a product due to reduction in yield, a catalyst whose activity has been reduced can be frequently exchanged for a new catalyst. However, an increase in the number of times for exchanging the catalyst is not preferable for industrial production. This is because costs on the catalyst are increased and because productivity is reduced if a production apparatus is stopped for exchange of catalyst. Further, in order to remove an active component which has been leached from a generated product, complicated purification steps such as rinsing and distillation are needed. Therefore, a production apparatus needs to be provided with an additional step. In such points, the conventional methods are not preferable in terms of industrial production. Accordingly, in the above-mentioned catalyst an active component needs to hardly leach. Further, the catalyst needs to maintain an excellent catalyst activity for a long time even if in the presence of water and an impurity such as free fatty acid (FFA). In these points, the catalyst has room for contrivance.